Sen. John McCain, the Republican Party's presumptive nominee for president, arrived in Baghdad on Sunday for an surprise visit with Iraqi and American diplomatic and military leaders, a U.S. official said.

A defiant supporter of the 2003 U.S.-led invasion and President Bush's troop increase last year, McCain has touted last year's drop in sectarian violence as a turning point in five-year war.

The details of his visit were not being released for security reasons. The trip was not announced, and he was believed to have been in the country for several hours before reporters were able to confirm his presence.

"Senator McCain is in Iraq and will be meeting with Iraqi and U.S. officials," said Mirembe Nantongo, spokesperson for the U.S. Embassy in Baghdad.

The Arizona senator was expected to meet with Iraqi Prime Minister Nouri al-Maliki and Gen. David Petraeus, the top U.S. military commander in Iraq.

"We were informed that John McCain landed in Iraq Sunday morning. A meeting will take place with the Iraqi government," said Ali al-Moussawi, an official in the Iraqi prime minister's office.